Daylight Saving Time and the Circadian Rhythm: Why You Feel Tired and How to Adapt Quickly

When the clocks move forward by one hour in spring, your watch changes instantly, but your biological clock does not. You may wake according to the new social time while your cells, hormones and sleep rhythm still follow the previous light-dark schedule. Morning grogginess, reduced concentration, poorer exercise performance and difficulty falling asleep are therefore not merely a lack of willpower. They are expected consequences of temporary circadian misalignment.

What happens to your body after the spring time change?

The spring transition to daylight saving time advances social time by one hour, but it does not advance solar time or your circadian rhythm at the same moment. Work, school, alarms and meals suddenly occur one hour earlier in relation to the sun.

Before the change, waking at 7:00 may have corresponded to a certain level of morning light, body temperature and hormonal readiness. After the clocks move forward, the new 7:00 occurs at what your body previously recognised as 6:00.

Your schedule demands wakefulness, but the biological processes that prepare you to wake may still be running according to the earlier timing.

This mismatch can affect:

• Morning alertness: the brain may still be closer to its biological night.
• Cortisol timing: the normal morning rise may not align perfectly with the new alarm time.
• Body temperature: the daily rise associated with wakefulness may occur later.
• Melatonin decline: nighttime melatonin may remain elevated closer to waking.
• Sleep duration: people often go to bed at a similar biological time but must wake one hour earlier.
• Exercise performance: coordination, motivation and perceived effort may temporarily worsen.

The clock change is therefore similar to a small phase advance. Phase advances are commonly more difficult than delays because the body must become sleepy and wake earlier than it naturally did before.

Why does the biological clock follow light instead of clock time?

The master circadian clock is located in the suprachiasmatic nucleus, or SCN, in the hypothalamus. It receives information about environmental light from specialised retinal cells containing the photopigment melanopsin.

The SCN does not know that a government or phone network has changed the official time. It reads photons reaching the eyes and compares the timing of light and darkness with its internal molecular rhythm.

Morning light helps the SCN coordinate:

• the morning rise in alertness,
• cortisol timing,
• the daily increase in body temperature,
• the decline of nighttime melatonin,
• the timing of sleepiness later that evening,
• peripheral clocks in organs and tissues.

When you wake earlier after the spring transition, natural light may still be weaker than it was at the same clock time before the change. In the evening, daylight also extends one hour later according to the clock.

The result is a double signal that can delay adaptation:

• Less morning light at the new waking time, when an earlier signal would be useful.
• More evening light at the new bedtime, when the body needs darkness to move sleep earlier.

This is why the light environment matters more than simply forcing yourself into bed one hour earlier.

For a broader explanation, read our guide to circadian rhythm, the SCN and biological time.

Why do you feel tired even after enough time in bed?

Time in bed and biological sleep timing are not the same thing. You may spend seven or eight hours in bed while waking during a circadian phase in which melatonin, body temperature and sleep pressure still favour continued sleep.

This creates the familiar feeling of being awake because the alarm rang, but not biologically ready to begin the day.

The first nights after the clock change can also become shorter. Many people do not feel sleepy one hour earlier, so bedtime changes little while the alarm moves forward.

Even a modest reduction in sleep may affect:

• reaction time,
• decision-making,
• mood and patience,
• appetite regulation,
• training motivation,
• perceived exercise intensity,
• driving performance.

The fatigue is therefore produced by two overlapping factors:

1. Acute sleep loss caused by waking earlier.
2. Circadian misalignment between social time and internal biological time.

Sleeping longer on the weekend may reduce accumulated sleep debt, but a very late weekend wake-up can also delay the biological clock again. A reasonably stable wake-up time is usually more helpful during the adaptation period.

Does the body fully adapt to daylight saving time?

Research indicates that adaptation is more complicated than feeling normal again after several days. Subjective tiredness may improve, while the relationship between sleep timing, dawn and biological time can remain altered throughout the daylight saving period.

A large European study led by Thomas Kantermann analysed data from approximately 55,000 people. Under standard time, sleep timing on free days followed the seasonal progression of dawn. Under daylight saving time, this relationship was disrupted.

A second part of the study followed 50 people for eight weeks around the spring and autumn transitions. Sleep and activity adjusted readily after the return to standard time in autumn, but activity timing did not fully adjust after the spring move to daylight saving time, particularly among later chronotypes.

The study therefore concluded that the human circadian system does not simply accept daylight saving time as if the sun had moved.

This does not mean that everyone remains visibly exhausted for the entire summer. Behaviour, social pressure and repeated alarms can make the new schedule feel normal. The deeper timing relationship between the body and solar light may nevertheless remain less aligned.

You can adapt behaviour to a new clock faster than you can move the sun. That is the central biological problem created by daylight saving time.

Why are evening chronotypes affected more strongly?

People with a later chronotype naturally become sleepy and wake later, making a forced one-hour phase advance more difficult. They already tend to receive less morning light and more evening light than early chronotypes.

The spring transition intensifies both tendencies. A later person must wake earlier in relation to their biological night, while the longer light-filled evening can make early sleep even less likely.

Later chronotypes may experience:

• greater morning sleep inertia,
• more difficulty falling asleep at the new bedtime,
• larger differences between weekday and weekend sleep,
• stronger reliance on caffeine,
• more pronounced social jet lag.

Social jet lag is the mismatch between the timing preferred by your biological clock and the timing demanded by work, school or family responsibilities.

Daylight saving time can amplify that mismatch because social schedules move while dawn does not.

Does the time change affect health and performance?

The spring transition is associated with short-term changes in sleep, alertness, cardiovascular events, mood and accident risk. These associations do not mean that every individual faces a major event, but they show that a one-hour disruption can have measurable population-level consequences.

A review of the available evidence reported associations between daylight saving time transitions and cardiovascular events, particularly during the first days after the spring change. Proposed mechanisms include sleep loss, sympathetic activation, hormonal disruption and circadian misalignment.

The American Academy of Sleep Medicine has also stated that the acute transition to daylight saving time introduces health and safety risks. Its position supports permanent standard time because morning light under standard time is more closely aligned with human circadian biology.

Practical consequences can include:

• Lower morning concentration during work or school.
• Reduced reaction speed when driving.
• Greater perceived effort during training.
• Increased irritability after shortened sleep.
• Changes in appetite and stimulant use.
• More difficulty maintaining an early bedtime because evening light lasts longer.

Which three steps help the body adapt faster?

The most effective strategy is to use light and routine to move the biological clock earlier. The original article focuses on three simple actions: morning outdoor light, protection from evening blue and green light, and a stable sleep-wake schedule.

1. Seek outdoor light soon after waking

Go outside as soon as practical after waking, ideally within the first 30 minutes. Morning light is the strongest environmental signal for advancing the circadian rhythm and communicating that the biological day has begun.

Outdoor light is usually much brighter than normal indoor lighting, including on a cloudy morning. A window reduces part of the spectrum and the total intensity, so being outside is preferable.

A practical starting point is:

• Bright clear morning: approximately 5 to 10 minutes outdoors.
• Cloudy morning: approximately 10 to 20 minutes outdoors.
• Very dark or overcast conditions: approximately 20 to 30 minutes outdoors.

Do not stare directly at the sun. Simply remain outdoors with your eyes open and allow the natural environment to fill your visual field.

A short walk adds movement and helps establish a repeatable morning routine.

Jaroslav also described using a 15-minute morning walk without his phone during the first days after the time change. He noticed better morning energy and earlier sleep onset within approximately three days. This is a personal observation, not a guaranteed clinical result, but it illustrates how a simple routine can reinforce the morning signal.

2. Reduce blue and green light after sunset

To move sleep earlier, protect the final hours of the evening from bright blue-rich artificial light. Melanopsin is highly sensitive to short-wavelength visible light, including blue and part of the green spectrum.

Phones, tablets, televisions and cool white LED bulbs can therefore tell the brain that daytime is continuing, even when the clock says it is late.

After sunset or during the final 90 minutes before sleep:

• dim overhead lighting,
• reduce screen brightness,
• use red evening bulbs,
• avoid holding bright screens close to the eyes,
• wear effective red lenses when screens remain necessary.

The Mitochondriak® indoor lighting range includes red evening bulbs and other solutions designed without blue and green light.

The Blue light blocking glasses Mitochondriak® use red lenses for evening protection from both blue and green wavelengths.

3. Keep the wake-up time consistent

A stable wake-up time gives your circadian system a repeatable anchor. Waking at the same time allows morning light, movement, breakfast and other daily signals to occur within a predictable window.

Try to maintain the new wake-up time for at least seven to ten days, including the weekend. A small variation is not a problem, but sleeping several hours later can pull the rhythm back toward a later phase.

Do not force sleep aggressively. Instead:

• dim the evening environment earlier,
• reduce stimulating activities,
• keep meals earlier and consistent,
• allow sleepiness to arrive naturally,
• wake at the planned time and seek morning light again.

If you become sleepy earlier than expected during the first days, treat that as useful feedback. Your body may be beginning to align with the advanced schedule.

A practical seven-day adjustment plan

Consistency matters more than one perfect morning. The following plan combines the three core actions into a simple week-long routine.

Repeat this pattern for at least one week. Evaluate not only whether you fall asleep faster, but also morning alertness, mood, appetite, training performance and reliance on caffeine.

Frequently asked questions about daylight saving time

How long does it take to adapt to daylight saving time?

The strongest fatigue often improves within several days, especially when sleep duration is protected. However, research suggests that the deeper relationship between sleep timing and solar dawn may remain altered throughout daylight saving time. Later chronotypes often adapt less completely than earlier chronotypes.

Is it normal to feel tired for a week after the time change?

Yes. A one-hour phase advance can shorten sleep and force waking during an earlier biological phase. Fatigue, poorer concentration and morning grogginess for several days are common. Persistent or severe fatigue lasting beyond the adjustment period may have another cause and deserves further attention.

Can morning light help me adapt faster?

Yes. Morning light is the strongest natural signal for advancing the circadian rhythm. Go outdoors as soon as practical after waking and repeat the routine daily. Bright morning light is more effective than normal indoor lighting because outdoor intensity is usually substantially higher.

Can melatonin help with the spring time change?

Melatonin can influence circadian timing, but its effect depends strongly on dose and timing. Taking it at the wrong biological time may be ineffective or shift the rhythm in an unwanted direction. Begin with light hygiene and a stable schedule. Discuss supplemental melatonin with a qualified healthcare professional, particularly if you take medication, are pregnant or have a medical condition.

What is social jet lag?

Social jet lag is the mismatch between your preferred biological sleep timing and the schedule imposed by work, school or social obligations. Daylight saving time can worsen this mismatch because social time advances while sunrise remains tied to solar time.

Why am I tired during the day but unable to fall asleep earlier?

You may have lost sleep because of the earlier alarm while your circadian clock still promotes sleepiness according to the old schedule. Bright evening light can delay melatonin and make the new bedtime even harder. Morning outdoor light and darker evenings address both sides of the problem.

Do blue light blocking glasses help after the time change?

Red blue light blocking glasses can reduce blue and green light reaching the retina during the evening. This helps prevent artificial lighting and screens from extending the daytime signal. They are most useful after sunset or during approximately the final 90 minutes before sleep.

Is permanent daylight saving time healthier than standard time?

Sleep and circadian organisations generally favour permanent standard time because it provides earlier morning light and aligns social schedules more closely with solar time. Permanent daylight saving time delays winter sunrise and may increase long-term circadian misalignment.

Sources and references

1. Kantermann T, Juda M, Merrow M, Roenneberg T. The human circadian clock's seasonal adjustment is disrupted by daylight saving time. Current Biology. 2007. PubMed
2. Manfredini R, Fabbian F, Cappadona R, et al. Daylight saving time and acute myocardial infarction: a meta-analysis. Journal of Clinical Medicine. 2018. PubMed
3. Rishi MA, Ahmed O, Barrantes Perez JH, et al. Daylight saving time: an American Academy of Sleep Medicine position statement. Journal of Clinical Sleep Medicine. 2020. PubMed
4. Dijk DJ, Beersma DGM, Daan S, Lewy AJ. Bright morning light advances the human circadian system without affecting NREM sleep homeostasis. American Journal of Physiology. 1989. PubMed
5. Samková L, Vondrasová D, Hájek I, Illnerová H. A fixed morning awakening coupled with a low intensity light maintains a phase advance of the human circadian system. Neuroscience Letters. 1997. PubMed
6. Chang AM, Aeschbach D, Duffy JF, Czeisler CA. Evening use of light-emitting eReaders negatively affects sleep, circadian timing and next-morning alertness. Proceedings of the National Academy of Sciences. 2015. PubMed